From the general state of the art, valve arrangements for controlling hydraulic drives are known, in which the control openings for controlling the supply and the outflow of the hydraulic drive are mechanically or hydraulically connected with each other. However, such valve arrangements have the disadvantage that they have a poor energetic efficiency. Further, to avoid cavitation, a plurality of valves will be required, depending on the effective direction of a load acting upon the hydraulic drive, which makes the complete valve arrangement effort demanding and expensive. As a solution to this problem, EP 0 809 737 B1, U.S. Pat. No. 5,138,838, U.S. Pat. Nos. 5,568,759 and 5,960,695 suggest valve arrangements, with which the supply and the outflow of the hydraulic drive can be controlled separately. These solutions, however, do not meet the heavy requirements with regard to low leakage flows of the working connections, when the valves are not activated. With these valve arrangements, the undesirable leakage flows at the working connections can only be avoided by means of at least two bi-directional or more than four unidirectional electromechanical valve drives, which increases the total costs of the valve arrangement and thus also the manufacturing costs.
The task of the invention is to improve the above-described valve arrangement in such a manner that it is intrinsically tight, and at the same time the valve arrangement shall have a relatively simple design.